The present invention generally relates to devices and processes for downhole separation of mixtures of water, oil, and gas within well bores.
In hydrocarbon production from subterranean formations, a production stream generally contains crude oil and/or hydrocarbon gases as the principal valuable products. Nevertheless, depending on the production well, water is often mixed in with valuable production streams. Water may be naturally present in a formation and may be present due to secondary recovery operations to enhance recovery of oil and gas such as artificial steam injection into the formation. Often, the water and oil will be present in the production stream as an oil-in-water emulsion (i.e. the water forms a continuous phase and the oil a dispersed phase) or a water-in-oil emulsion (i.e. the oil forms a continuous phase and the water is a dispersed phase). Furthermore, gas, when present, may exist as a separate dispersed phase (i.e. as bubbles). Some of the gas will normally be dissolved in the liquid phases, the amount of dissolved gas varying according to the temperature and pressure of the stream at any point in question.
Thus, mixtures of oil, water, and various gases are often encountered in subterranean formations. Typically, these phases are separated uphole after extracting the production streams to the surface. Numerous methods of three phase separation are used including the use of uphole separation equipment such as flash drums, gravity separators, and cyclonic separators.
Flash drums are vessels into which a stream is reduced in pressure sufficiently to flash gases from a liquid stream. Gravity separators are essentially vessels or drums into which a mixture is introduced and allowed to settle. Gravity causes the denser water phase to settle to form a layer at the bottom of the separator, and the less dense oil phase to form a liquid layer on top of the water layer. Hydrocarbon gas, if present as a dispersed phase (bubbles), may separate from the water and oil and fill the atmosphere in the space above the liquid phase layer. Water, oil, and gas can be tapped off periodically or continuously from their respective layers. Cyclonic separators are separators utilizing centrifugal force to effect separations of phases sufficiently close in density that separation by gravity separation is either ineffective or too time-consuming.
Conventional multi-phase separation equipment uphole is typically expensive, inefficient, and cumbersome. Examples of uphole separation devices include the devices disclosed in U.S. Pat. No. 7,147,788. In particular, conventional separation equipment is typically sized to process certain quantities and ratios of gas/oil and water/oil. Furthermore, conventional equipment is often bulky and poses additional environmental and safety hazards to personnel at the surface when separation operations are performed uphole.